IRS is one of the most promising performance-enhancement technologies for next-generation wireless networks to improve both the spectral efficiency and the energy efficiency of the wireless communication systems [1]}. An IRS is basically a planar array which consists of a large number of passive phase shifters that reconfigure the wireless propagation environment by inducing phase shifts on the impinging electromagnetic waves [2]}, [3]}.
It has been shown that IRS is compatible with many communication techniques, e. g. millimeter-wave, Terahertz communications, physical layer security, simultaneous wireless information and power transfer (SWIPT), unmanned aerial
vehicle networks (UAV), MIMO systems and finally, NOMA [4]}, [5]}, [6]}, [7]}. Most papers assume that the IRS lacks active elements, thus it is incapable of pilot-based channel estimation.
Hence, in most IRS-assisted system designs, it is assumed that the cascaded AP-IRS-user channels are available at the AP, because the estimation of IRS-related channels separately is difficult. Furthermore, in some recent works, the effects of channel estimation error on the performance of the IRS is considered and robust designs have been proposed to cope with this issue [8]}, [9]}, [10]}. Thus, in this paper, we attempt to design a robust IRS-aided NOMA communication system.
